The present invention relates to an electronic ballast for a cold cathode fluorescent lamp. Cold cathode fluorescent lamps are typically employed, for example, as background lamps for liquid crystal displays used, for example, in personal computer displays. In the prior art, with reference to FIG. 1, a flat panel display comprising an LCD display 10 has a cold cathode fluorescent lamp behind the display to provide back lighting. A separate power supply 20 is typically employed and is connected to a source of AC power via an AC power plug 22. An interconnecting cable 24 interconnects the power supply 20 and the display 10.
The power supply 20, as shown in FIG. 2, includes an AC to DC converter which converts the input AC voltage, typically 90 to 265 volts AC 50/60 Hz, to a lower DC voltage, for example 24 volts DC. The 24 volts DC power is supplied by the interconnect cable 24 to the display 10. Internally in the display a buck converter 12 regulates the current and supplies the regulated current 14 to the Royer output stage 16, which comprises a switching circuit which provides the necessary voltage to the cold cathode fluorescent lamp (CCFL) indicated at 18. The ignition voltage is Kv. A dimming control 13 may be provided to regulate the brightness level of the CCFL 18.
It would be desirable to eliminate the external power supply as well as to reduce the size of the internal power conversion circuitry in the display to save cost, weight and space and to provide greater efficiency.